In order to support a case where cooling operation and heating operation of indoor units are mixed, and other cases, a simultaneous cooling-heating multi-air conditioner includes cooling-heating switching units installed between the outdoor unit and the indoor units for switching pipes connected to indoor gas pipes, between a high-pressure gas pipe and a low-pressure gas pipe.
Here, in the case where it is not preferable that high-temperature and high-pressure gas refrigerant flow into an indoor unit in cooling operation, in non-operation, in the heating thermo-off state, or in blow operation, the indoor gas pipe is connected to the low-pressure gas pipe using the cooling-heating switching unit, and the circuit on the high-pressure gas pipe side is closed.
Closing the circuit on the high-pressure gas pipe side as described above may cause gas refrigerant in a high-pressure gas branch pipe of the cooling-heating switching unit, which is now closed, to condense and turn into liquid refrigerant. If gas refrigerant is flowing, no condensation occurs. However, since the high-pressure gas branch is closed, condensation of the gas refrigerant occurs.
If condensation of gas refrigerant occurs in a high-pressure gas branch pipe of a cooling-heating switching unit, the amount of refrigerant circulating in the entire air conditioner becomes deficient, causing a problem that the refrigerant for heating operation of other indoor units becomes deficient.
To prevent liquid refrigerant from accumulating in the high-pressure gas branch pipe of the cooling-heating switching unit as above, Patent Literature 1 discloses a technique of slightly opening an expansion valve on the high-pressure gas pipe side of the cooling-heating switching unit of an indoor unit in which heating operation is not operated or suspended, and opening the expansion valve on the low-pressure gas pipe side to collect the refrigerant when the room temperature becomes a predetermined temperature. Patent Literature 1 also discloses a technique of connecting a bypass capillary tube instead of slightly opening the expansion valve on the high-pressure gas pipe side.